High-voltage, field-effect transistors (HVFETs) are well known in the semiconductor arts. Many HVFETs employ a device structure that includes an extended drain region that supports or blocks the applied high-voltage (e.g., several hundred volts) when the device is in the “off” state. In a conventional vertical HVFET structure, a mesa or pillar of semiconductor material forms the extended drain or drift region for current flow in the on-state. A trench gate structure is formed near the top of the substrate, adjacent the sidewall regions of the mesa where a body region is disposed above the extended drain region. Application of an appropriate voltage potential to the gate causes a conductive channel to be formed along the vertical sidewall portion of the body region such that current may flow vertically through the semiconductor material, i.e., from a top surface of the substrate where the source region is disposed, down to the bottom of the substrate where the drain region is located.
In a traditional layout, a vertical HVFET consists of long continuous silicon pillar structure that extends across the semiconductor die, with the pillar structure being repeated in a direction perpendicular to the pillar length. One problem that arises with this layout, however, is that it tends to produce large warping of the silicon wafer during high temperature processing steps. In many processes, the warping is permanent and large enough to prevent the wafer from tool handling during subsequent processing steps. Additionally, gate oxide weakness in the rounded end portions of the transistor layout can result in gate oxide breakdown voltage and reliability problems.